Magnetic Resonance Imaging (MRI) apparatus employed in parallel MRI (pMRI) may acquire signals in parallel using an array of detectors (e.g., coils). The detectors may be arranged in a phased array of coils. Signals received at the coils are used in reconstruction. Reconstruction quality may depend on the amount of data made available by the coils. Reconstruction quality may also depend on understanding the actual sensitivity and spatial encoding capabilities of a coil(s) during an MRI session so that the signals can be meaningfully processed. Thus, additional auto-calibration signal (ACS) lines may be acquired during certain types of pMRI and used to calibrate the coils. Auto-calibrating refers to calibration of the coil sensitivities at the time of image acquisition.
Conventionally, only actual signals received from actual coils have been used for reconstruction. However, additional information useful for image reconstruction may have been available through conjugate symmetry. Conventional conjugate symmetry methods, to the extent they were used at all, required high resolution information about the background phase. Since this information was difficult to obtain, this limited the use of conjugate symmetry.